Hide out of stock related products in WooCommerce

Question

In WooCommerce I would like to hide Out of Stock products from Related products in single product pages. Is it possible?

Any track is appreciated.

Answer 1

UPDATE 2021

You can use the following:

add_filter( 'woocommerce_product_related_posts_query', 'alter_product_related_posts_query', 10, 3 );
function alter_product_related_posts_query( $query, $product_id, $args ){
    global $wpdb;

    $query['join']  .= " INNER JOIN {$wpdb->postmeta} as pm ON p.ID = pm.post_id ";
    $query['where'] .= " AND pm.meta_key = '_stock_status' AND meta_value = 'instock' ";
    
    return $query;
}

Code goes in functions.php file of your active child theme (or active theme).

Now we need to remove "related products" cached data deleting the related transients to flush this cache (thanks to @Cody Rees).

There is 2 ways to do it:

1). The easiest way:

Go to admin Woocommerce > Status > Tools > WooCommerce transients and press on "Clear transcients".

2). The other way targeting specific related transients to be deleted:

Add the following code and save:

add_action('init', 'delete_related_products_cached_data');
function delete_related_products_cached_data() {
    global $wpdb;

    $wpdb->query("DELETE FROM {$wpdb->prefix}options WHERE `option_name` LIKE '_transient_wc_related_%'");
}

Code goes in functions.php file of your active child theme (or active theme).

Run it only once by browsing any page of your web site and remove it.